it all depends on how much data you have compressed onto your dvd-r, the more data the more compressed and the less quality, but all the titles i have backed up with dvd-shrink have been fine except lord of the rings rotk which was a bit jerky, but that was 2 disks compressed onto 1 dvd-r so its not suprising…
the grey bar on dvd shrink that you see before you press “back-up” has the percentage the disk will be compressed, if it drops below 50 you might see a difference but over that is always fine for me…
if you are concerned about quality use the re-author tool instead of backup on dvd-shrink and just copy the movie file with no extras or menus…

If you don’t need it, leave off the DTS audio track, as this can consume quite some room (up to about 1Gb)… yes that one is a gigantic space hog!

If you have very long moveis you want to fit on a single disc with a high picture quality, you may want to consider reeincoding. This is suite tedious etc… but it gives way better quality than transcoding does!